Thermal spraying method and apparatus for improved adhesion strength

ABSTRACT

A thermal spraying method includes the steps of: (1) preparing a speed-increasing means for adding energy to the heated material or the heating material to increase a flying speed of the material; and (2) adding energy to the heated material or the heating material by the speed-increasing means in such a manner that a flying speed of the heated material or the heating material increases until the material reaches a surface of an object.

TECHNICAL FIELD

[0001] The present invention relates to a thermal spraying method forincreasing adhesion strength of the thermal sprayed layer. The presentinvention relates to a thermal spraying apparatus and a powder passageapparatus which can be used in the thermal spraying method.

BACKGROUND ART

[0002] There has been developed a thermal spraying method for formingthermal sprayed layer in the industrial world. In the thermal sprayingmethod, material having a powder shape is heated in high temperatures,the heated material is sprayed and is piled up on a surface of an objectby thermal spraying. The thermal spraying advantageously increasesabrasion resistance and corrosion resistance of the object by thethermal sprayed layer. Also, Japanese Unexamined Patent Publications63-66900 and 5-5893 disclose a thermal spraying method which uses: anenergy source for flying material; and another energy source for heatingthe material by a laser beam and being independent of the energy source.According to this Publication techniques, the material for thermalspraying flys to the object, and the flying material is heated by thelaser beam running parallel with the surface of the object.

[0003] In the conventional thermal spraying method, the heated materialfor thermal spraying decreases in flying speed as it approaches theobject. Also, in the thermal spraying method concerning theabove-mentioned Publications, the heated material-for thermal sprayingdecreases in flying speed as it approaches the object. Therefore, thethermal spraying layer is not much improved in adhesion strength, evenwhen other spraying conditions are improved.

SUMMARY OF THE INVENTION

[0004] The present invention has been accomplished in view of theaforementioned circumstances. It is therefore an aim of the presentinvention to provide a thermal spraying method for improving adhesionstrength of a thermal sprayed layer. It is therefore another aim of thepresent invention to provide a thermal spraying apparatus for using thepresent invention method and for improving adhesion strength of athermal sprayed layer. Also, it is therefore still another aim of thepresent invention to provide a powder passage apparatus which can beused in carrying out the present invention method and can suppresspowder material from being stopped in a passage.

[0005] According to a first aspect of the present invention, a thermalspraying method for producing a thermal sprayed layer by heatingmaterial for thermal spraying, by flying the heated material or theheating material to a surface of an object, and by piling the heatedmaterial on the surface of the object, comprises the steps of:

[0006] (1) preparing a speed-increasing means for adding energy to theheated material or the heating material to increase a flying speed ofthe material; and

[0007] (2) adding energy to the heated material or the heating materialby the speed-increasing means in such a manner that a flying speed ofthe heated material or the heating material increases until the materialreaches the surface of the object.

[0008] According to a second aspect of the present invention, a thermalspraying apparatus for producing a thermal sprayed layer by heatingmaterial for thermal spraying, by flying the heated material or theheating material to a surface of an object, and by piling the heatedmaterial on the surface of the object, comprises:

[0009] (1) a passage-forming member for forming a passage through whichmaterial for thermal spraying passes;

[0010] (2) a heating means for heating the material passing through thepassage-forming member or discharged from the passage-forming member;and

[0011] (3) a speed-increasing means for increasing a flying speed ofheated material.

[0012] According to a third aspect of the present invention, a powderpassage apparatus comprises:

[0013] (1) a conductive coil having conductivity, and having an axis anda plurality of loops disposed substantially coaxially with respect tothe axis; and

[0014] (2) a passage-forming member disposed along the axis of theconductive coil for supplying material for thermal spraying.

[0015] According to the first aspect of the present invention, until theheated material reaches the surface of the object, energy is added tothe heated material or the heating material by the speed-increasingmeans in such a manner that a flying speed of the heated materialincreases. Accordingly, the material for thermal spraying collidesagainst the object at a high speed. So, the thermal sprayed layer isimproved in adhesion strength.

[0016] Also, in a preferable mode, the flying speed of the material isincreased in comparison with that of heating position. In other words,in a preferable mode, the flying speed of the material at the heatingposition, namely, the flying speed before the acceleration, is lowerthan that of the material after the acceleration. This mode can lengthenthe time for heating the material for thermal spraying, therebyenhancing ability for heating the material for thermal spraying to hightemperatures.

[0017] According to the second aspect of the present invention, athermal spraying apparatus comprises: (1) a passage-forming member forforming a passage through which material for thermal spraying passes;(2) a heating means for heating the material passing through thepassage-forming member or discharged from the passage-forming member;and (3) a speed-increasing means for increasing a flying speed ofmaterial. So, the thermal spraying apparatus according to the secondaspect can be used in carrying out the first aspect of the presentinvention, thermal spraying method. Accordingly, the material forthermal spraying collides against the object at a high speed, and thethermal sprayed layer is improved in adhesion strength. Preferably, thespeed-increasing means increases the flying speed of the material thanthat of the material during heating.

[0018] According to the third aspect of the present invention, thepowder passage apparatus comprises: a conductive coil, havingconductivity, and having an axis and a plurality of loops disposedsubstantially coaxially with respect to the axis. Also, thepassage-forming member is disposed along the axis of the conductivecoil. So, the apparatus according to the third aspect can be used inheating the material for thermal spraying by means of induction heating.Induction heating is advantageous in heating the material for thermalspraying in a short time, and in controlling heating temperature.

[0019] Further, according to the third aspect of the present invention,when electricity is supplied to the conductive coil, it is suppressedthat the material for thermal spraying adheres to the inner surface ofthe passage of the passage-forming member. The reason is as follows: Theconductive coil generates magnetic force along the central axis line ofthe passage, namely, along the central axis line of the conductive coil.So, the powder material for thermal spraying, having permeability,easily flows along the center portion in a radial direction of thepassage.

PREFERABLE MODE OF THE INVENTION

[0020] According to the first aspect of the present invention, until theheated material reaches the surface of the object, energy is added tothe flying material by a speed-increasing means in such a manner that aflying speed of the material increases. When the flying speed of thematerial for thermal spraying is increased, the material collidesagainst the object at a high speed, adhesion of the material isimproved, and the thermal sprayed layer is improved in adhesionstrength.

[0021] According to the preferable mode of this invention, the adding ofthe energy for increasing the flying speed of material is carried outafter the heating of the material. That is to say, after the materialfor thermal spraying is heated, the flying speed of the material isincreased. The heating before increasing the flying speed of thematerial can lengthen the time which is required for heating thematerial.

[0022] Or, according to the thermal spraying method for concerninganother preferable mode of the first invention, the flying speed of thematerial can be increased during the heating of material. Also, thethermal spraying method concerning the first invention rarely allows theflying speed of the material to be increased before the heating ofmaterial.

[0023] The material for thermal spraying may be in a form of particle,when it flies to the object. The flying form of particle may be in asolid form, in a melting form, or in a partially melting form. The formof material before thermal spraying may be in a powder state, in a wirestate, or in a rod state. When the form of material is powder, theaverage diameter of particle of the material is decided on occasion. Theupper limit of average diameter of the particle may be for example 100μm, 200 μm, 300 μm or 500 μm. The lower limit of average diameter of theparticle is for example 1 μm, 10 μm or 40 μm. Therefore, the averagediameter of particle of the material may be in a range of 1-500 μm, in arange of 10-300 μm, or in a range of 40-200 μm. The average diameter ofparticle is not limited within these.

[0024] The material for thermal spraying is preferably metal, especiallymetal powder. When the material for thermal spraying is metal, it hasconductivity. Also, many metals have good magnetic permeability. Themetal may have, in the ordinary temperature range, ferromagnetism orparamagnetism. Concretely, the metal constituting the material forthermal spraying may be ferrous such as cast iron, carbon steel,stainless steel, or alloy steel. Also, the metal constituting thematerial for thermal spraying may be non-ferrous—at least one selectedfrom the group consisting of aluminum, aluminum alloy, copper, copperalloy, nickel, nickel alloy, titanium, or titanium alloy. Sometimes, thematerial for thermal spraying may be ceramics, cermet mixing ceramicswith metal. Ceramics may be oxide, nitride, carbide or boride. Ceramicsmay be at least one selected from the group consisting of alumina,silica, magnesia, silicon carbide, silicon nitride, boride titanium andso on. Even when the material for thermal spraying is formed ofceramics, until the material reaches the object, the energy is given tothe material in such a manner that the flying speed of the material isincreased, impact speed of the material is increased, and the materialcollides against the object at a high speed. Therefore, the thermalsprayed layer is advantageously improved in adhesion strength.

[0025] When the material for thermal spraying is formed of ceramics, theinduction heating is not obtained in the material unlike metal. Forceramics does not have conductivity substantially. In case where thepassage through which the material for thermal spraying passes is formedof carbon tube, the carbon tube can be heated by induction heating, andthe material for thermal spraying in the carbon tube is heated byradiant heat from the carbon tube.

[0026] According to a preferable mode, the heating of material iscarried out by a first energy source, and the adding of energy forincreasing the flying speed of material is carried out by a secondenergy source. Also, according to another preferable mode, the firstenergy source have one path and another path for transmitting energythereof, the heating of material is carried out by the one path of thefirst energy source, and the adding of energy for increasing the flyingspeed of the material is carried out by the another path of the firstenergy source. The first energy source is not restricted in kinds. So,the first energy source can be a flame-generating means for generating aflame of fuel (acetylene and propane, etc.)-oxygen, a plasma-flamegenerating means for generating a plasma flame, a laser means forgenerating a laser beam, or an induction heating means for heating thematerial for thermal spraying by induction heating. The inductionheating means includes the case in which the passage or thepassage-forming member is induction-heated and the material is heated byradiant heat of the heated passage or the heated passage-forming member.

[0027] The present invention permits the case in which the heating ofthe material for thermal spraying is carried out by using the firstenergy source, and the increasing of flying speed of the material forthermal spraying is carried out by using the second energy sourcesunlike the first energy source. This case allows the first energy sourceand the second energy source to be controlled independently andindividually. So, this case allows the heating of material and theincreasing of the flying speed of material to be controlledindependently and individually. Therefore, this case can enlarge anadjustable range in temperature and flying speed of the material forthermal spraying. Accordingly, this case can select a mode in which thetemperature of material is high and the flying speed of material ishigh, another mode in which the temperature of material is low and theflying speed of material is high, or still another mode in which thetemperature of material is high and the flying speed of material is low.

[0028] The present invention permits the case in which the heating ofmaterial is carried out by the one path of the first energy source, andthe adding of energy for increasing the flying speed of material iscarried out by the another path of the first energy source. This caseallows the heating of material and the increasing of flying speed of thematerial to be controlled. This case can enlarge an adjustable range intemperature and flying speed of the material for thermal spraying.

[0029] The first energy source is not restricted in kinds for heatingthe material. The first energy source can be a flame-generating meansfor generating a flame of fuel (acetylene and propane)-oxygen, aplasma-flame generating means for generating a plasma flame, or a lasermeans for generating a laser beam. In a preferable mode, a material forthermal spraying has conductivity and magnetic permeability, and thefirst energy source may be constituted by an induction heating means forheating the material for thermal spraying. The induction heating meanscan control the degree of heating of the material—low temperature,medium temperature or high temperature—by adjusting frequencies ofalternating current, current value, electric power, etc. Thespeed-increasing means may be a means which uses a swelling gas pressureobtained by expanding gas or by evaporating liquid in short time—forexample, by evaporating liquid with the laser beam.

[0030] Thermal spraying apparatus concerning the second aspect includes:(1) a passage-forming member for forming a passage through which thematerial for thermal spraying passes; (2) a heating means for heatingthe material passing through the passage-forming member or dischargedfrom the passage-forming member; and (3) a speed-increasing means foradding energy to the material for thermal spraying to increase a flyingspeed of the material and to accelerate the flying speed of thematerial. The speed-increasing means may increase the flying speed ofthe material than that of the material during heating. The heating meansfor concerning the thermal spraying apparatus of the second aspect maybe a flame-generating means for generating flame of fuel (acetylene andpropane)-oxygen, a plasma flame generating means for generating plasmaflame, a laser means for generating a laser beam, or an inductionheating means for heating the material for thermal spraying.

[0031] The thermal spraying apparatus concerning the above mentionedsecond aspect can be used in carrying out the first aspect of thepresent invention method, increasing the flying speed of the materialfor thermal spraying.

[0032] The powder passage apparatus concerning the third aspectcomprises: (1) a conductive coil having conductivity and having an axisand a plurality of loops disposed substantially coaxially with respectto the axis; and (2) a passage-forming member disposed along the axis ofthe conductive coil for supplying material for thermal spraying.

[0033] According to the powder passage apparatus concerning the thirdaspect, when powder material has magnetic permeability, it is suppressedthat the powder material for thermal spraying adheres to the innersurface of the passage of the passage-forming member. The reason is asfollows: when current is supplied to the conductive coil, the conductivecoil generates magnetic force along the central axis line of theconductive coil. So, the powder material for thermal spraying, havingmagnetic permeability, easily flows along the center portion in a radialdirection of passage under the influence of the magnetic force. In thecase where the material for thermal spraying is powder, when the powderpassage apparatus concerning the third aspect is used as a powderpassage apparatus of the thermal spraying apparatus, it is suppressedthat the powder material for thermal spraying adheres to the innersurface of the passage. Therefore, this can suppress abnormal blockageof the material for thermal spraying in the passage. So, this cansuppress inequality in heating the powder material for thermal spraying.Thus, the powder material for thermal spraying is uniformly heated asmuch as possible to high temperature, and the thermal sprayed layer isadvantageously improved in adhesion strength.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The present invention will now be shown and described in terms ofconcrete embodiments thereof with reference to the appended drawings, inwhich:

[0035]FIG. 1 is related to a first embodiment, and schematically shows aconfiguration in which material is sprayed by a thermal sprayingapparatus;

[0036]FIG. 2 is related to a first embodiment, and schematically showsan internal construction of a gun constituting the thermal sprayingapparatus;

[0037]FIG. 3 is related to the first embodiment, and shows a graph whichexpresses selectivity between temperature of material particles andflying speed of the material particles;

[0038]FIG. 4 is related to a comparison embodiment, and shows a graphwhich expresses selectivity between temperature of material particlesand flying speed of the material particles;

[0039]FIG. 5(A) is related to a comparison embodiment, and shows aphotograph which expresses a sedimentation form of particlesconstituting a thermal spraying layer;

[0040]FIG. 5(B) is related to a comparison embodiment, and shows amagnified photograph which expresses a sedimentation form of particlesconstituting a thermal spraying layer;

[0041]FIG. 6 is related to a second embodiment, and shows aconfiguration which schematically expresses conditions in which materialis thermal-sprayed by a thermal spraying apparatus;

[0042]FIG. 7 schematically shows a powder passage apparatus which heatsthe material for thermal spraying by means of induction heating, andmeasures temperature of the particle material for thermal spraying;

[0043]FIG. 8 shows a graph which expresses a relationship betweenfrequency of alternating current supplied to a conductive coilconstituting an induction heating coil and temperature of particlematerial;

[0044]FIG. 9 shows a graph which expresses a relationship betweenfrequency of alternating current supplied to a conductive coilconstituting an induction heating coil and temperature of particlematerial;

[0045]FIG. 10 shows a graph which expresses a relationship between gaspressure and gas speed;

[0046]FIG. 11 shows a graph which expresses a relationship between gastemperature and gas speed;

[0047]FIG. 12 shows a graph which expresses a relationship between typesand speed of the gas;

[0048]FIG. 13 shows a graph which expresses a relationship betweenparticle speed and particle temperature in each thermal spraying form;

[0049]FIG. 14 shows a graph which expresses porosity of the thermalsprayed layer in each thermal sprayed layer;

[0050]FIG. 15 shows a graph which expresses adhesion strength of thethermal sprayed layer produces by each thermal spraying form; and

[0051]FIG. 16 shows a graph which expresses hardness of the thermalsprayed layer produces by each thermal spraying form.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The first PreferredEmbodiment

[0052] The first preferred embodiment will hereinafter be explainedbased on the accompanying FIGS. 1-5. First, a thermal spraying apparatusof the present embodiment will be explained. As shown in FIG. 1, thethermal spraying apparatus has a passage-forming member 1, a heatingmeans 5 (a first energy source), and a speed-increasing means 7 (asecond energy source). The passage-forming member 1 forms a passagethrough which material passes having a powder shape for thermalspraying. The heating means 5 heats the material in the passage of thepassage-forming member 1 for thermal spraying. The speed-increasingmeans 7 increases a flying speed of the material for the thermalspraying in comparison with the flying speed in a heating position 30 kbased on the heating means 5.

[0053] The passage-forming member 1 concerning the thermal sprayingapparatus has a gun 2 working as a first passage-forming member forminga first passage 20, and a second passage-forming member 3 having atubular shape and forming a second passage 30 for supplying the materialfor thermal spraying. The gun 2 includes: a gun body 22 having a highpressure room 23 which is communicated with the first passage 20; and anozzle 25 disposed at the head of the gun body 22 and having a nozzlehole 24 which is communicated with the high pressure room 23. The nozzle25 is formed of a “Laval nozzle” used for a supersonic gas streamapparatus such as jet engine. As shown in FIG. 2, the high pressure room23 and the first passage 20 is disposed coaxially around the secondpassage 30. The first passage 20 of the gun 2 surrounds an exit 31 ofthe second passage 30.

[0054] As shown in FIG. 1, the second passage-forming member 3 connectsa powder feeder 8 with the gun 2. The powder feeder 8 contains acontainer 81 having a powder room 80, material 82 having a powder shapefor thermal spraying stored in the container 81, and a pressure portion83 for increasing an internal pressure of the powder room 80. Thematerial 82 for thermal spraying is formed of ferrous powder havingconductivity and magnetic permeability, and it is to be heated byinduction heating. The ferrous powder is Fe-C alloy.

[0055] When the pressure of gas such as air is applied to the powderroom 80 of the container 81 by way of the pressure portion 83, thematerial 82 in the container 81 flies through the second passage 30 ofthe second passage-forming member 3 to the gun 2, it is discharged fromthe exit 31 formed at the top end of the second passage 30, and inaddition, it is blown forward by way of the first passage 20 and thenozzle 25 of the gun 2. The heating means 5 heats the material forthermal spraying by using electricity. The heating means 5 is disposedat a heating position 30 k located in the exit 31 of the second passage30. This heating means 5 contains a conductive coil 51 and feeding means52. The conductive coil 51 works as an induction heating coil, beingdisposed by jig 2 a at the heating position 30 k inside the gun 2. Thefeeding means 52 supplies current, alternating current having a highfrequency to the conductive coil 51 by way of a feeding line 52 f. Thefeeding means 52 is constituted by a high frequency oscillator forgenerating alternating current of high frequency. The conductive coil 51works as an induction heating coil, being the induction heating means.The conductive coil 51, having a coil shape, is formed of a plurality ofloops 51 a connected to each other in series.

[0056] As shown in FIG. 2, the conductive coil 51 is placed outside thesecond passage 30 and substantially coaxially with respect to the secondpassage 30. That is to say, the conductive coil 51 surrounds the exit 31of the second passage-forming member 3 which forms the second passage30. Therefore, it is thought that the supplying of current to theconductive coil 51 generates magnetic force along the central axis lineof the second passage 30, namely, along the central axis line of theconductive coil 51.

[0057] The parts being surrounded by the conductive coil 51, in thesecond passage-forming member 3, can be formed of non-electro-conductivesubstance such as the silica-based substance, or electro-conductivesubstance such as carbon-based substance. The non-electro conductivesubstance such as silica-based substance is not substantiallyinduction-heated. The electro-conductive substance such as carbon-basedsubstance is induction-heated, it becomes a high temperature, forinstance over 1500° C. and over 2000° C., it can transmit radiant heatto the powder material for thermal spraying which passes through thesecond passage 30, and it can heat the material for thermal spraying tohigh temperatures by the radiant heat.

[0058] The inside diameter of the second passage 30 is decidedconsidering factors such as passing ability and heating of the powdermaterial for thermal spraying. The inside diameter of the second passage30 may be, for example, in a range of 0.5-20 mm, in a range of 1-10 mm,and in a range of 1-5 mm. The inside diameter is not limited to theseranges.

[0059] The speed-increasing means 7 is formed by using a second energysource being independent of the first energy source. As shown in FIG. 1,the speed-increasing means 7 includes: a gas-storing division 70 formedby a gas bomb which encloses high pressure gas; a compressor 71connected with the gas-storing division 70 by way of a middle passage 70a; and a pressure amplifier 72 connected with the compressor 71 by wayof a middle passage 71 a. The pressure amplifier 72 has a heating unit73, such as electric heaters, for heating the gas supplied from thecompressor 71.

[0060] The gas being contained in the gas-storing division 70 iscontinuously supplied to the compressor 71. The gas is compressed by thecompressor 71. Afterward, the gas is supplied to the pressure amplifier72, and it is continuously heated to high temperature in the heatingunit 73 of the pressure amplifier 72. Therefore, the gas expands, andthe swelling pressure of the gas becomes high pressure. In short, thepressure of the gas is amplified. The high-pressurized gas iscontinuously supplied to the high pressure room 23 of the gun 2 throughthe middle passage 72 a, it becomes a high speed gas stream, and it iscontinuously blown forward from the nozzle 25 by way of the firstpassage 20 of the gun 2.

[0061] The type of gas being contained in the gas-storing division 70,namely, the type of the high speed gas stream for increasing the flyingspeed of the material for thermal spraying is not restricted—for exampleat least one selected from the group consisting of inert gas such ashelium gas, nitrogen gas, air gas, oxygen gas, hydrogen gas, etc. Thepreferable mode selects gas whose molecular weight is small—for examplethe helium gas—in view of obtaining the high-speed gas stream generatedby using the swelling gas pressure based on gas expansion. Also, air gasis preferable in view of cost.

[0062] It is desirable that the surface 90 of the object 9 for thermalspraying is carried out by roughening treatment. The rougheningtreatment may be blasting—for example shot blasting treatment, gridblasting treatment, etc. The material of the object 9 can be selected onoccasion—generally metal. The metal of object 9 may be at least one ofnon-ferrous alloy or ferrous alloy. The non-ferrous alloy may bealuminum, aluminum alloy, copper, copper alloy, titanium, titaniumalloy, etc. The ferrous alloy may be cast iron, carbon steel, stainlesssteel, alloy steel, etc. The object 9 may be sliding parts, pistons,cylinder blocks, cylinder heads, etc.—it is not restricted in usage.

[0063] Next, as shown in FIG. 1, thermal spraying will be explained. Theobject 9 is placed in the front of the nozzle 25 of the gun 2. Thenozzles 25 of the gun 2 faces to the object 9 at a fixed distance. Thefeeding means 52 feeds current to the conductive coil 51. The current isalternating current having a high frequency. The frequency is decideddepending on kinds of the material for thermal spraying, material kindsof the object 9, cost for the feeding means 52, etc. For example, as forfrequency of the alternating current to the conductive coil 51, theupper limit may be for example 5000 kHz, 20 MHz or 100 MHz, and thelower limit is for example 5 kHz, 20 kHz and 100 kHz or 200 kHz. Thefrequency is not limited to these.

[0064] In thermal spraying, the pressure of gas such as air is appliedto the powder room 80 of the container 81 by way of the pressure portion83. The powder material for thermal spraying in the container 81 issupplied to the second passage 30 of the second passage-forming member3. In addition, the powder material for thermal spraying flows to theexit 31 of the second passage 30 of the second passage-forming member 3,and it is blown forward from the nozzle 25 by way of the first passage20 of the gun 2. The powder material for thermal spraying isinduction-heated to high temperature in a short time by the conductivecoil 51, when it passes near the exit 31 of the second passage 30,namely, the heating position 30 k.

[0065] Temperature of the material for thermal spraying is decideddepending on frequencies of alternating current of the conductive coil51—over 500° C., over 800° C., over 1000° C., over 1500° C., over 1700°C., over 2000° C. or over 2400° C., as appreciated from FIGS. 8 and 9.

[0066] According to the present embodiment, in thermal spraying, the gasstored in the gas-storing division 70 is continuously supplied by thecompressor 71, it is compressed by the compressor 71, and it is heatedto high temperature in the heating unit 73 of the pressure amplifier 72.As a result, the gas is amplified in pressure, and it is continuouslysupplied to the high pressure room 23 of the gun 2, and thereby it isblown forward from the nozzle 25 as a high speed gas stream. Therefore,after the material is heated to the high temperature by the conductivecoil 51 at the heating position 30 k, it is discharged from the exit 31of the second passage 30 as the high speed gas stream. The high speedgas stream forces the material for thermal spraying to accelerate theflying speed. The high speed gas stream flows from the high pressureroom 23 to the nozzle 25. In short, the flying speed of the material forthermal spraying is increased at the nozzle 25 than at the heatingposition 30 k to be heated by the conductive coil 51. That is to say,according to the present embodiment, the energy is given to the materialfor thermal spraying in such a manner that the material for thermalspraying is increased in the flying speed in the gun 2, until thematerial reached the object 9.

[0067] The material being increased in flying speed collides against thesurface 90 of the object 9 at a high speed. As a result, the materialfor thermal spraying is piled on the surface 90 of the object 9 to forma thermal sprayed layer 92. The flying speed of the material is decideddepending on kinds of the material for thermal spray and kinds of thepressure amplifier 72—for example over 400 m/sec, over 500 m/sec, over600 m/sec, over 700 m/sec, over 800 m/sec, or over 900 m/sec—below 3000km/sec. The flying speed of the case having the speed-increasing means 7may be 1-70 times or 5-70 times as large as that of the case not havingthe speed-increasing means 7.

[0068] According to the present embodiment, the speed-increasing means 7forces the material for thermal spraying in such a manner that thematerial for thermal spray is increased in the flying speed until thematerial reaches the object 9. Therefore, the material for thermalspraying collides against the surface 90 of the object 9 at a highspeed. So, the thermal sprayed layer 92 is increased in adhesionstrength.

[0069] According to the present embodiment, the flying speed of theaccelerated material is increased in comparison with that thereof atheating position 30 k. In other words, the flying speed of the materialat the heating position 30 k, before the acceleration, is lower thanthat of the material after the acceleration. Therefore, the presentembodiment can lengthen the time for heating the material for thermalspraying to a target temperature range, thereby ensuring ability forheating the material for thermal spraying.

[0070]FIG. 5(A) shows a photograph concerning to a sample of the thermalsprayed layer formed on the object 9. FIG. 5(B) shows a magnifiedphotograph. As shown in FIGS. 5(A) and 5(B), it is understood that theparticles of the material accelerated to high speed encroached upon thesurface of the object in such a manner that the particles of material islocated inside the surface of the object. Therefore, the thermal sprayedlayer is improved in adhesion strength. The reason is acceleration inthe flying speed of the material for thermal spraying.

[0071] The heating of the material for thermal spraying is carried outby the conductive coil 51 which works as the induction heating means—thefirst energy source. The increasing of flying speed of the material iscarried out by the speed-increasing means 7—the second energy source,being different from the first energy source. Therefore, the presentembodiment allows the conductive coil 51 for heating the material to becontrolled independent of the speed-increasing means 7 for acceleratingthe material. So, the present embodiment allows the accelerating of thematerial to be controlled independent of the heating of the material.Therefore, this can enlarge a range for adjusting temperature and speedof the material for thermal spraying in comparison with the conventionalthermal spraying.

[0072]FIG. 3 shows a control model. As shown in FIG. 3, the presentembodiment allows temperature of the material for thermal spraying to beadjusted between temperature “T1” exhibiting low temperature andtemperature “T2” exhibiting high temperature. Also, the presentembodiment allows speed of the material for thermal spraying to beadjusted between speed “V1” exhibiting low speed and speed “V2”exhibiting high speed. Therefore, the present embodiment is advantageousin enlarging an adjustable range of temperature and speed for thematerial for thermal spraying, and in obtaining the thermal sprayedlayer having the desired characteristics.

[0073] By the way, “M1” of FIG. 4 shows an adjustable range oftemperature and speed of the material for thermal spraying in the plasmaspraying method used, the conventional technique. “M2” of FIG. 4 showsan adjustable range of temperature and speed of the material for thermalspraying in HVOF (High Velocity oxygen-Fuel) thermal spraying, theconventional technique. In the conventional plasma spraying method,heating and flying of the material for thermal spraying are carried outby a common energy source of the plasma flame. In the conventional HVOFthermal spraying, heating and flying of the material for thermalspraying are carried out by a common energy source of gas combustion,and the particle flying speed of HVOF thermal spraying is faster thanthat of the plasma spraying method.

[0074] In the conventional plasma spraying method, as shown by “M1” ofFIG. 4, temperature of the material for thermal spraying is lowered, asflying speed of the material for thermal spraying is increased. Also,temperature of the material for thermal spraying is raised, as flyingspeed of the material for thermal spraying is decreased. In theconventional HVOF spraying method, as shown by “M2” of FIG. 4,temperature of the material for thermal spraying is lowered, as flyingspeed of the material for thermal spraying is increased. Also,temperature of the material for thermal spraying is raised, as flyingspeed of the material for thermal spraying is decreased. The plasmaspraying method and the HVOF thermal spraying concerning conventiontechniques have a limit for enlarging the adjustable range oftemperature and flying speed of the material for thermal spraying.

[0075] According to the present embodiment, the conductive coil 51 heatsthe ferrous material for thermal spraying having a powder shape whichpasses the second passage 30 of the second passage-forming member.According to the induction heating, when frequency of alternatingcurrent of the conductive coil 51 is adjusted, heating temperature ofmaterial for thermal spraying can be easily adjusted in a considerablerange, as shown in FIGS. 8 and 9. That is to say, the present embodimentcan easily adjust heating temperature of the material for thermalspraying in a considerable range so as to improve adhesion strength ofthe thermal sprayed layer. In this meaning, induction heating isadvantageous in improving characteristic property, such as adhesionstrength, of thermal sprayed layer.

[0076] It is suppressed that the material for thermal spraying adheresto the inner surface of the second passage 30 of the secondpassage-forming member 3, when current is supplied to the conductivecoil 51. This fact is confirmed based on the test by the presentinventors. The reason is as follows. The conductive coil 51 generatesmagnetic force along the central axis line of the second passage 30,namely, along the central axis line of the conductive coil 51. So, thepowder material for thermal spraying easily flows along the centerportion in the radial direction of second passage 30. Still, theneighborhood of the exit 31 of the second passage 30 constitutes thepowder passage apparatus concerning the third aspect.

Second Preferred Embodiment

[0077] The second embodiment will be explained with FIG. 6. The secondembodiment is fundamentally similar to the first embodiment inconstruction, action and effect. First, the thermal spraying apparatusof the present embodiment will be explained. As shown in FIG. 6, thethermal spraying apparatus contains: a passage-forming member 1 forforming a passage through which ferrous powder material for thermalspraying passes; a heating means 5B for heating the ferrous powdermaterial which is supplied through the passage-forming member 1, and aspeed-increasing means 7B. The speed-increasing means 7B increases theflying speed of the material for thermal spraying in comparison with theflying speed in heating position based on the heating means 5B.

[0078] The passage-forming member 1 concerning the thermal sprayingapparatus has a gun 2 working as a first passage-forming member having afirst passage 20, and a second passage-forming member 3 having a tubularshape and having a second passage 30 for supplying the material.

[0079] The second passage-forming member 3 connects a powder feeder 8with the gun 2. The powder feeder 8 contains a container 81 having apowder room 80, material 82 having a powder shape for thermal sprayingbeing stored in the container 81, and a pressure portion 83 forincreasing an internal pressure of the powder room 80. When the gaspressure is applied to the powder room 80 of the container 81, thepowder material stored in the container 81 flows to the gun 2 throughthe second passage 30 of the second passage-forming member 3.

[0080] The heating means 5B heats the material in the second passage 30for thermal spraying using the laser beam which is high-density energybeam exhibiting the first energy source. The heating means 5B is formedby the laser oscillator which discharges a laser beam 53 x with highenergy density such as YAG laser beam and CO2 laser beam. The path oflaser beam 53 x, constituting one path, is connected to a heatingposition 30 k of the second passage 30. So, when the powder material forthermal spraying passes through the second passage 30 of the secondpassage-forming member 3, it is heated by laser beam 53 x (one path)discharged by the heating means 5B to the target temperature range.

[0081] The speed-increasing means 7B is constituted to use gas pressureto be increased by the laser beam 53 y (another path) being separatedfrom the laser beam 53 x corresponding to the first energy source. Thatis to say, the speed-increasing means 7B contains a beam splitter 55, acontainer 56 containing evaporating substance 57 (it is generally aliquid for vaporization), and a pump 58. The beam splitter 55 splits thelaser beam 53 y from the laser beam 53 x in order to send the laser beam53 y to an irradiation portion 23 w in the high pressure room 23 of thegun 2. The pump 58 works as an evaporating substance feeding means whichcontinuously supplies the evaporating substance 57 to the irradiationportion 23 w in the high pressure room 23 of the gun 2 by way of afeeding line 58 a. The evaporating substance 57 may be formed bydispersing fine particles in liquid. The liquid may be at least one ofwater, alcohol, organic solvents, etc. The fine particles have goodabsorbability with respect to the laser beam. The fine particle, such ascarbon particles, may be formed of substance having good absorbabilitywith respect to the laser beam. When the evaporating substance 57 isirradiated with by laser beam 53 y (another path), it is gasified in amoment.

[0082] According to the present embodiment, the pump 58 supplies theevaporating substance 57 to the irradiation portion 23 w disposed in thehigh pressure room 23 of the gun 2 by way of the feeding line 58 a. Theirradiation portion 23 w in the gun 2 is irradiated with the laser beam53 y which is split by the beam splitter 55 as another path. Theevaporating substance 57 includes the fine particles having goodabsorbability withe respect to the laser beam, and it is gasified in amoment to high temperature. According to the present embodiment, thepump 58 supplies the evaporating substance 57 continuously to theirradiation portion 23 w of the high pressure room 23, and the laserbeam 53 y being split by the beam splitter 55 is continuously dischargedto the evaporating substance 57 in the irradiation portion 23 w of thehigh pressure room 23. So, the evaporating substance 57 is continuouslygasified to generate the high speed gas stream in the high pressure room23. The high speed gas stream is blown forward from the nozzle 25 by wayof the first passage 20 of the gun 2. This gives energy to the materialfor thermal spraying discharged from the exit 31 of the second passage30. Accordingly, this accelerates the material for thermal sprayingdischarged from the exit 31 of the second passage 30 in flying speed. Asa result, this increases the flying speed of the material for thermalspraying discharged from the exit 31 of the second passage 30 incomparison with that of the heating position 30 k.

[0083] So, the material collides against the surface 90 of the object 9at a high speed to be piled up. Therefore, thermal sprayed layer 92 isformed on the surface 90 of the object 9. According to the presentembodiment, the speed-increasing means 7B forces the material forthermal spraying to accelerate in such a manner that the material forthermal spray is increased in flying speed until the material reachesthe object 9. Therefore, the material for thermal spraying collidesagainst the surface 90 of object 9 at a high speed. So, thermal sprayedlayer 92 is increased in adhesion strength.

[0084] According to the present embodiment, the flying speed of theaccelerated material is increased in comparison with that of the heatingposition 30 k. In other words, the flying speed of the material at theheating position 30 k, before the acceleration, is lower than that ofthe material just after the acceleration. Therefore, the presentembodiment can lengthen the time for heating the material for thermalspraying to a target temperature range, thereby ensuring ability forheating the material for thermal spraying.

EXAMPLES

[0085] Next, examples carried out by the present inventors will beexplained.

Example 1

[0086]FIG. 7 shows the powder passage apparatus concerning Example 1. InExample 1, a silica tube 95 was disposed vertically and coaxially withrespect in the central region of a conductive coil 51, and theconductive coil 51 was placed vertically for working as inductionheating coil. The silica tube 95 constitutes a passage-forming member.In this condition, the present inventors: fell the metallic powdernaturally from a funnel 96 disposed at an upper side of the conductivecoil 51; and measured temperature of the metallic powder, namely,material for thermal spraying discharged from a lower end of the silicatube 95 by use of a measuring device 97. The measuring device 97measured temperature and flying speed of the particle.

[0087] In Example 1, the present inventors varied the frequency of thealternating current of the conductive coil 51 in a range of 10 kHz-10000kHz (10 MHz). The metallic powder was iron-carbon alloy havingconductivity and magnetic permeability, having a carbon content of 1mass % (1 weight %), and having a particle size of 50-90 μm.

[0088]FIG. 8 shows the test result. As shown in FIG. 8, with theincrease of the frequency of the alternating current which was fed tothe conductive coil 51, the particle temperature of the powderdischarged from the lower end of the silica tube 95 became hightemperature. Concretely, powder particle temperature was about 300° C.when frequency was 100 kHz. Powder particle temperature was about 1000°C. when frequency was 400 kHz. Powder particle temperature exceeded2000° C. when frequency was 10000 kHz. It is understood that thefrequency of the alternating current of the conductive coil 51 ispreferable over 400 kHz or 1000 kHz for raising the particletemperature, based on the result of FIG. 8.

[0089] In Example 1, the present inventors have confirmed that themetallic powder flows along the central axis of the silica tube 95 inthe case where current is supplied to the conductive coil 51 incomparison with the case where current is not supplied to the conductivecoil 51. When direct current is supplied to the conductive coil 51, thesimilar fact is obtained.

Example 2

[0090] In Example 2, a carbon tube was used instead of the silica tube95 in FIG. 7, the present inventors measured the temperature of thepowder discharged from the lower end of the carbon tube by use of themeasuring device 97. The present inventors varied frequency ofalternating current in a range of 10 kHz-10000 kHz (10 MHz). Theconductive coil 51 was vertically disposed, having a central axis linepositioned perpendicularly. The metal powder of Example 2 was the sameas that of Example 1.

[0091]FIG. 9 shows the test result. As shown in FIG. 9, with theincrease of frequency of alternating current supplied to the conductivecoil 51, the particle temperature of powder became high temperature.Concreatly, powder particle temperature was about 400° C. when frequencywas 100 kHz. The powder particle temperature was about 1500-1600° C.when the frequency was 400 kHz. Powder particle temperature was about2000° C. when frequency was 2000 kHz. Powder particle temperatureexceeded 3000° C. when frequency exceeded 3000 kHz. Based on FIG. 9, itis understood that frequency is preferably over 400 kHz or 1000 kHz toraise powder particle temperature.

[0092] In Example 2, the carbon tube for supplying the metallic powderwas placed in the central region of the conductive coil 51. So, thecarbon tube was induction-heated to high temperature of red heatcondition or white heat condition. That is to say, depending onfrequency and electric energy, the temperature of carbon tube itselfbecame over 1000K, 1500K, 2000K or 2500K. Therefore, the metal powderwas heated not only by induction-heating because of the conductive coil51 but also by radiation heat because of the heated carbon tube so as toincrease efficiency for heating.

[0093] Investigation

[0094] The present inventors required a relationship between gaspressure in front of “Laval nozzle” and speed of gas blown from “Lavalnozzle”,on the basis of the calculation. FIG. 10 shows this result. InFIG. 10, characteristic line “SHe” shows the result in using helium gas,and characteristic line “SAir” shows the result in using air gas. Asshown at characteristic line “SAir” of FIG. 10, gas speed was about 500m/sec when air gas was used, gas speed was about 500 m/sec when gaspressure was 1 MPa. Gas speed was about 600 m/sec when gas pressure was3 MPa. However, as shown at characteristic line “SHe” of FIG. 10, inusing helium gas, when gas pressure is 0.5 MPa, gas speed isconsiderably high-speed, exceeding 1000 m/sec. Further, as shown atcharacteristic line “SHe” of Further 10, gas speed exceeded 1300 m/secwhen gas pressure was 1 MPa, and gas speed exceeded 1400 m/sec when gaspressure was 2 MPa. It is appreciated that helium gas is more effectivethan air gas to increase gas speed.

[0095] The present inventors required a relationship between speed andtemperature of gas blown from “Laval nozzle” based on calculation. FIG.11 shows this result. In FIG. 11, characteristic line “PHe” shows theresult in using helium gas, and characteristic line “PAir” shows theresult in using air gas. The speed of gas blown from the nozzlegradually increases when gas temperature is high, as shown fromcharacteristic lines “PAir” and “PHe” of FIG. 11. Therefore, it isappreciated that high temperature of gas is effective for increasing theflying speed of the material for thermal spraying.

[0096] As shown at characteristic line “PAir” of FIG. 11, in using airgas, when gas temperature was 400-800K, the gas speed was 600 m/sec-900m/sec. However, in using helium gas having a low molecule weight, asshown at characteristic line “PHe” of FIG. 11, when the gas temperaturewas 400K, the gas speed exceeded 1500 m/sec, being high-speed. As shownat characteristic line “PHe” of FIG. 11, when the gas temperature was600K, gas speed exceeded 2000 m/sec, being high-speed. When gastemperature was 800K, gas speed exceeded 2100 m/sec, being high-speed.Also, characteristic line “PHVOF” in FIG. 11 shows the gas speed of theconventional HVOF thermal spraying method. As understand from thecomparison between characteristic lines “PHe” and “PHVOF” in FIG. 11, inusing helium gas, when gas temperature was over 400K, the gas speed washigher than that of the conventional HVOF method.

[0097] Further, the present inventors: respectively selected gas fromthe group consisting of hydrogen gas (H2), helium gas (He), nitrogen gas(N2), air gas, oxygen gas (O2), argon gas (Ar); and required the speedof gas, at a temperature of 300 K, to be blown from the nozzle the gun2, based on calculation. FIG. 12 shows these results. As shown in FIG.12, gas speed was high when molecular weight of gas was small. It isappreciated that helium gas, having a low molecular weight, is effectivein increasing the flying speed of the powder material for thermalspraying.

Example 3

[0098] The present inventors carried out thermal spraying actually basedon the conditions shown in Table 1. In this case, the object had apolished surface, and was preheated at 100° C. TABLE 1 comparisonexample 1 Particle temperature and particle speed in comparison example{circle over (1)} are similar to those of plasma flame thermal sprayingbeing used as a conventional technique. comparison example 2 Particletemperature and particle speed in comparison example {circle over (2)}are similar to those of HVOF thermal spraying being used as aconventional technique. comparison example 3 Particle temperature andparticle speed in comparison example {circle over (3)} are lower thanthose of plasma flame thermal spraying and HVOF thermal spraying beingused as a conventional technique. comparison example 4 Particletemperature is higher in comparison example {circle over (4)} than thatof plasma flame thermal spraying and HVOF thermal spraying being used asa conventional technique, and particle speed is lower in comparisonexample {circle over (4)} than that of plasma flame thermal spraying andHVOF thermal spraying. present embodiment 5 Particle temperature andparticle speed in present embodiment {circle over (5)} are higher thanthose of plasma flame thermal spraying and HVOF thermal spraying beingused as a conventional technique. present embodiment 6 Particletemperature is lower in present embodiment {circle over (6)} than thatof plasma flame thermal spraying and HVOF thermal spraying being used asa conventional technique, and particle speed is higher in presentembodiment {circle over (6)} than that of plasma flame thermal sprayingand HVOF thermal spraying.

[0099]FIG. 13 shows testing conditions of Table 1. As shown in FIG. 13,in testing condition {circle over (1)}, the particle temperature inthermal spraying was about 2800K and the particle speed was about 240m/sec. In testing condition {circle over (2)}, the particle temperaturewas about 2000K and the particle speed was about 400 m/sec. In testingcondition {circle over (3)}, the particle temperature was about 1800Kand the particle speed was about 200 m/sec. In testing condition {circleover (4)}, the particle temperature was about 3400K and the particlespeed was about 160 m/sec. Testing conditions {circle over (1)} arecorrespondent to comparison examples. The speed of testing conditions{circle over (5)} and {circle over (6)} were to be high speed, beingcorrespondent to the present embodiment. In testing condition {circleover (5)}, particle temperature were as high as 3600K, being hightemperature, and the particle speed was as high as 620 m/sec. In testingcondition {circle over (6)} concerning the present embodiment, theparticle temperature was as low as below 1000K, and the particle speedwas as high as about 780 m/sec. Particle temperature and particle speedwere obtained by the measuring device 97, namely, a device for measuringtemperature and speed of thermal spraying particle.

[0100] In addition, the present inventors measured porosity by an imageprocessing in laser microscope and adhesion strength of the thermalsprayed layer formed on the basis of Table 1 and FIG. 13. In this case,the object 9 was made of aluminum alloy (JIS-AC2C), and the material forthermal spraying was made of iron-carbon alloy powder (carbon: 1 mass %)produced by gas atomization to have a thickness of 0.2 mm.

[0101] In measuring adhesion strength, the present inventors used testspecimens covered with the thermal sprayed layer, added an externalforce to the thermal sprayed layer by a punch along an interface betweenthe thermal sprayed layer and the object 9, and obtained adhesionstrength based on the external force when the thermal sprayed layer wasexfoliated. FIG. 14 shows the test result of porosity. FIG. 15 shows thetest result of adhesion strength of thermal sprayed layer.

[0102] As shown in FIG. 14, testing conditions {circle over (1)}{circleover (3)} and {circle over (4)} concerning comparison examples showedporosity as large as over 8%. Testing condition {circle over (3)} showedporosity as large as over 20%—it is thought that the particle speed isslow and the particle temperature is low. Testing conditions {circleover (5)} and {circle over (6)} concerning the present embodiment showedporosity as small as 2% or less—it is thought that the thermal sprayedlayer is fine in structure because speed of thermal spraying is fast.

[0103] Also, as shown in FIG. 15, as for testing conditions {circle over(1)}{circle over (2)}{circle over (3)} and {circle over (4)} concerningcomparison example, adhesion strength of the thermal sprayed layer wasnot satisfied. As for testing condition {circle over (3)}, adhesionstrength is as low as about 34 MPa—it is thought that the particle speedis slow and the particle temperature is low. As for testing conditions{circle over (5)} and {circle over (6)} concerning the presentembodiment, adhesion strength of the thermal sprayed layer exceeded 100MPa, being high. It is thought that the particle speed is high.

[0104] In comparison with testing conditions {circle over (5)} and{circle over (6)} concerning the present embodiment, test condition{circle over (6)} exhibited excellent adhesion strength which is nearthat of testing condition {circle over (5)}, although particletemperature as low as about 800K. From this fact, it is thought that theincreasing of the flying speed of the powder material for thermalspraying is effective to increase adhesion strength of the thermalsprayed layer.

Example 6

[0105] The present inventors required hardness of the thermal sprayedlayer formed based on the conditions of Table 1 and FIG. 13, by use ofVickers hardness test(load: 0.098N(10 gf)). In this case, the materialfor thermal spraying was iron-carbon alloy powder (carbon: 1 mass %)produced by water atomization. The material before thermal spraying hadorganization formed of bainitic structure, and hardness was about Hv600.FIG. 16 shows the result of hardness of the thermal sprayed layer. Incase of the thermal sprayed layer produced in testing condition {circleover (6)} concerning the present embodiment, the hardness of thermalsprayed layer exceeded Hv50O. The reason why the hardness exceeds Hv500is as follows: In case of the thermal sprayed layer produced in testingcondition {circle over (6)}—in spite of particle speed as high as over700 m/sec—since particle temperatures are as low as about 800K, thethermal spraying powder is not melted to easily keep organization andcharacteristics before thermal spraying.

[0106] Additional Remarks

[0107] It is possible to also grasp next technical thought from theabove mentioned description.

[0108] According to each claims, wherein the flying speed of thematerial for thermal spraying is over 600 m/sec, over 700 m/sec or over800 m/sec.

[0109] According to each claims, wherein adhesion strength (shearadhesion strength) of the thermal sprayed layer is over 90 MPa, over 100MPa, over 110 MPa or over 120 MPa.

[0110] According to each claims, wherein particle temperature ofmaterial for thermal spraying is over 2000K, and particle speed ofmaterial for thermal spraying is over 600 m/sec, over 700 m/sec or over800 m/sec.

[0111] According to each claims, wherein particle temperature ofmaterial for thermal spraying is over 3000K, and particle speed ofmaterial for thermal spraying is over 600 m/sec, over 700 m/sec or over800 m/sec.

[0112] According to each claims, wherein particle temperature ofmaterial for thermal spraying is below 1500K or below 1000K, andparticle speed of material for thermal spraying is over 600 m/sec, over700 m/sec or over 800 m/sec.

[0113] A gun for thermal spraying comprising: a passage for supplyingthe material for thermal spraying, and a high pressure room forincreasing the flying speed of heated material for thermal spraying.

[0114] A thermal spraying apparatus comprising: (1) a gun having apassage for supplying the material for thermal spraying, and a highpressure room for increasing the flying speed of heated material forthermal spraying; (2) an evaporating substance feeding means for feedingevaporating substance to a beam irradiation portion; and (3) a heatingmeans for discharging a high density energy beam (laser beam) to theevaporating substance supplied to the beam irradiation portion in thehigh pressure room for evaporating the evaporating substance in a shorttime.

[0115] A gun for thermal spraying comprising: a passage for supplyingthe material for thermal spraying; a heating means for heating thematerial for thermal spraying; and a high pressure room for increasingthe flying speed of heated material for thermal spraying.

[0116] A gun for thermal spraying comprising: a passage for supplyingthe material for thermal spraying, an induction heating means forinduction-heating the material for thermal spraying in the passage ordischarged from the passage.

[0117] A gun for thermal spraying comprising: a passage for supplyingthe material for thermal spraying, an induction coil forinduction-heating the material for thermal spraying in the passage ordischarged from the passage.

[0118] A powder passage apparatus for supplying powder, comprising: aconductive coil having conductivity, and having an axis and a pluralityof loops disposed coaxially with respect to the axis; a passage-formingmember disposed along the axis of the conductive coil and in theconductive coil for supplying material for thermal spraying; and whereinthe conductive coil generates magnetic force along the central axis lineof the passage, thereby the powder material for thermal spraying havingpermeability flows along the center portion in a radial direction of thepassage.

What is claimed is:
 1. A thermal spraying method for producing a thermalsprayed layer by heating material for thermal spraying, by flying theheated material or the heating material to a surface of an object, andby piling the heated material on the surface of the object, comprisingthe steps of: preparing a speed-increasing means for adding energy tothe heated material or the heating material to increase a flying speedof the material; and adding energy to the heated material or the heatingmaterial by the speed-increasing means in such a manner that a flyingspeed of the heated material or the heating material increases until thematerial reaches the surface of the object; wherein: the heating of thematerial is carried out by a first energy source capable of heating thematerial for thermal spraying, and the adding of the energy forincreasing the flying speed of the material is carried out by a secondenergy source constituting the speed-increasing means for adding energyto the heated material or the heating material, the second energy sourcebeing controlled independently of the first energy source, the firstenergy source for heating the material is constituted by an inductionheating apparatus for heating the material for thermal spraying by meansof induction heating based on alternating current having a highfrequency, and the speed-increasing means increases and accelerates theflying speed of material by a gas stream having a high speed, and thegas stream is formed of at least one selected from the group consistingof helium gas, nitrogen gas, air gas, oxygen gas, and hydrogen gas. 2.The thermal spraying method according to claim 1, wherein the adding ofthe energy for increasing the flying speed of the material is carriedout after the heating of the material for thermal spraying.
 3. Thethermal spraying method according to claim 1, wherein the adding of theenergy for increasing the flying speed of the material is carried outduring the heating of the material for thermal spraying.
 4. The thermalspraying method according to claim 1, wherein the first energy sourceand the second energy source are capable of being controlledindependently and individually to adjust the heating of the material andthe increasing of the flying speed of the material.
 5. The thermalspraying method according to claim 1, wherein the speed-increasing meansincludes a gas-storing division for increasing the flying speed of thematerial to store at least one selected from the group consisting ofhelium gas, nitrogen gas, air gas, oxygen gas, and hydrogen gas.
 6. Thethermal spraying method according to claim 1, wherein the material forthermal spraying has conductivity and magnetic permeability.
 7. Thethermal spraying method according to claim 1, wherein the frequency ofalternating current is set to be in a range from 5 kHz to 100 MHz. 8.The thermal spraying method according to claim 1, wherein the flyingspeed of the material is accelerated by the speed-increasing means, andwherein the flying speed of the material before acceleration is lowerthan that of the material after the acceleration for lengthening thetime for heating the material for thermal spraying to a targettemperature range, thereby ensuring ability for heating the material forthermal spraying.
 9. The thermal spraying method according to claim 1,wherein the speed-increasing means increases the flying speed of thematerial by using a swelling gas pressure caused by expanding gas or byevaporating liquid.
 10. The thermal spraying method according claim 1,wherein the speed-increasing means includes: a gun having a highpressure room; a gas-storing division for storing gas; a compressorconnected with the gas-storing division for compressing the gas suppliedfrom the gas-storing division; and a pressure amplifier connected withthe compressor for amplifying the pressure of the gas compressed by thecompressor; and wherein the amplified pressure is supplied to the highpressure room for obtaining the high pressure in the high pressure roomto increase the flying speed of the material.
 11. The thermal sprayingmethod according to claim 1, wherein the material for thermal sprayinghas a powder particle shape whose diameter falls in a range from 1 to500 μm.
 12. The thermal spraying method according to claim 1, whereinthe material for thermal spraying is formed of at least one selectedfrom the group consisting of as cast iron, carbon steel, stainlesssteel, alloy steel, aluminum, aluminum alloy, copper, copper alloy,nickel, nickel alloy, titanium, titanium alloy, ceramics, and cermet.13. The thermal spraying method according to claim 1, wherein saidspeed-increasing means comprises a gun, and said speed-increasing meansincreases the flying speed of the heated material or the heatingmaterial within said gun.
 14. A thermal spraying method for producing athermal sprayed layer by heating material for thermal spraying, byflying the heated material or the heating material to a surface of anobject, and by piling the heated material on the surface of the object,comprising the steps of: preparing a speed-increasing means for addingenergy to the heated material or the heating material to increase aflying speed of the material; and adding energy to the heated materialor the heating material by the speed-increasing means in such a mannerthat a flying speed of the heated material or the heating materialincreases until the material reaches the surface of the object; wherein:the heating of the material is carried out by a first energy sourcecapable of heating the material for thermal spraying, and the adding ofthe energy for increasing the flying speed of the material is carriedout by a second energy source constituting the speed-increasing meansfor adding energy to the heated material or the heating material, thesecond energy source being controlled independently of the first energysource, and the speed-increasing means includes a laser apparatus fordischarging a laser beam, increases the flying speed of the material bydischarging the laser beam to liquid having ability of absorption oflaser beam so as to evaporate the liquid for generating a swelling gaspressure.
 15. The thermal spraying method according to claim 15, whereinthe speed-increasing means includes: a gun having a high pressure roomcontaining an irradiation portion which is to be irradiated with a laserbeam; a beam splitter for splitting the laser beam from a main laserbeam in order to send the split laser beam to the irradiation portion ofthe high pressure room; a container for containing evaporatingsubstance, and a supplying means for supplying the evaporating substancefrom the container to the irradiation portion of the high pressure room;and wherein the evaporating substance supplied to the irradiationportion is irradiated with the laser beam to generate a swelling gaspressure in the high pressure room.
 16. The thermal spraying methodaccording to claim 15, wherein the first energy source for heating thematerial for thermal spraying is selected from the group consisting of aflame-generating means for generating a flame of fuel-oxygen, aplasma-flame generating means for generating a plasma flame, a lasermeans for generating a laser beam, and an induction heating means forheating the material for thermal by induction heating.